1. Field of the Invention
The present invention relates to a field emission type cathode, an electron emission apparatus and an electron emission apparatus manufacturing method.
2. Description of the Related Art
There have been proposed various types of electron emission apparatuses having field emission type cathodes, such as a planar display apparatus, i.e., a panel type display apparatus. As for an apparatus for making a bright image display, a cathode ray-tube type structure for striking an electron beam on the fluorescent surface of an image formation plane to thereby emit light, is normally adopted.
As proposed in, for example, Japanese Patent Application Laid-Open (JP-A) No. 1-173555, a conventional planar display apparatus of a cathode ray-tube type structure is such that a plurality of thermoelectron emission cathodes, i.e., filaments are provided to face a fluorescent surface, thermoelectrons generated by these cathodes and secondary electrons resulting from the thermoelectrons are allowed to direct toward the fluorescent surface and that according to an image signal an electron beam excites the respective colors on the fluorescent surface to cause light emission. In this case, as the image plane becomes larger in size, the filaments are provided in common for many pixels, that is, many red, green and blue fluorescent substance trio forming the fluorescent surface.
Accordingly, as the image plane becomes, in particular, larger in size, the arrangement and assembly of the filaments become more complicated.
Furthermore, to make the planar display apparatus of the cathode ray-tube structure small in size, the length of the electron gun is decreased and the deflecting angle of electrons is widened to shorten the depth dimension of the apparatus. However, since the image plane of a planar display apparatus is becoming wider in recent years, the development of thinner planar display apparatuses is desired.
In the meantime, as for the conventional planar display apparatus, there is proposed an apparatus using field emission type cathodes or so-called cold cathodes. The structure of an example of such planar type display apparatus will be described hereinafter with reference to the drawings.
The planar display apparatus 100 shown in FIG. 15 consists of a fluorescent surface 101, a planar white light emission display apparatus main body 102 having field emission type cathodes K arranged to face the fluorescent surface 101 and a planar color shutter 103 arranged to contact or face the front surface of the apparatus at the side at which the fluorescent surface 101 is arranged.
In the display apparatus main body 102, as shown in FIG. 15, a light transmitting front panel 104 and a back panel 105 face each other through a spacer (not shown) holding the panels 104 and 105 at predetermined intervals. The peripheral edges thereof are airtight sealed by glass frit or the like and a flat space is formed between the panels 104 and 105.
An anode metal layer 160 and the fluorescent surface 101 entirely coated with, for example, white light emission fluorescent material in advance are formed on the inner surface of the front panel 104. A metal back layer 106 such as an Al film as in the case of an ordinary cathode ray-tube is coated on the surface of the fluorescent surface 101.
On the other hand, many cathode electrodes 107 extending in perpendicular direction in, for example, a band-like manner are arranged in parallel to one another and coated on the inner surface of the back panel 105.
An insulating film 108 is coated on the cathode electrodes 107 and gate electrodes 109 extending to be almost orthogonal to the extension direction of the cathode electrodes 107, for example, horizontally are arranged in parallel to one another on the insulating film 108.
Holes 110 are formed at the crossings of the cathode electrodes 107 and the gate electrodes 109, respectively. In these holes 110, conical field emission type cathodes K are formed to be coated on the cathode electrodes 107, respectively.
Each of the field emission type cathodes K is made of a material, such as Mo, W and Cr, which emits electrons by a tunnel effect when applied with a field of, for example, about 106 to 107 (V/cm).
To help understand the configuration of a cathode structure including the field emission type cathode K, the gate electrode and the like which constitute the planar display apparatus 100 of the above-stated conventional structure, one example of the configuration as well as its manufacturing method will be described with reference to manufacturing step views shown in FIGS. 16 to 19.
First, as already described with reference to FIG. 15, cathode electrodes 107 are formed on the inner surface of the back panel 105 along one direction, e.g., vertical scan direction.
Each of the cathode electrode 107 is configured such that a metal layer made of, for example, Cr is formed entirely by deposition, sputtering or the like and selectively etched by photolithography, to thereby form the cathode electrode 107 into a predetermined pattern.
Next, as shown in FIG. 16, on the patterned cathode electrode 107, an insulating film 108 is coated on the entire surface thereof by sputtering or the like and a metal 111 such as high melting point metal of, for example, Mo or W, finally constituting a gate electrode 109 is formed on the insulating film 108 by deposition, sputtering or the like.
As shown in FIG. 17, a resist pattern made of, for example, a photoresist, though not shown therein, is formed. Using the resist pattern as a mask, anisotropic etching such as RIE (reactive ion etching) is conducted to the metal layer 111 to thereby form a band-shaped gate electrode 109 in a predetermined pattern, i.e., extending in the horizontal direction orthogonal to the extension direction of the cathode electrode 107 shown in FIG. 15. Also, a plurality of small holes 111h, for example, are provided at crossings of the gate electrodes 109 and the cathode electrodes 107, respectively.
Next, through these small holes 111h, chemical etching with which the gate electrode 109, that is, the metal layer 111 is not etched but the insulating layer 108 is isotropically etched, is conducted, thereby forming holes 112 each having a width larger than the width of the small hole 111h and a depth corresponding to the entire thickness of the insulating layer 108.
In this way, as shown in FIG. 15, holes 110 are formed out of the holes 112 and the small holes 111h at crossings of the cathode electrodes 107 and the gate electrodes 109, respectively.
Thereafter, as shown in FIG. 18, a metal layer 113 made of, for example, Al or Ni is coated on the gate electrode 109 by oblique deposition. The oblique deposition is carried out while rotating the back panel 105 in the plane, so that round holes 114 each having a conical inner periphery are formed around the small holes 111h, respectively.
In that case, the deposition of the metal layer 113 is carried out with a selected angle with which the metal layer 113 is not coated in the holes 112 through the small holes 111h. 
Through the round holes 114, a field emission type cathode material, that is, a metal, such as W or Mo, having a high melting point and a low work function is deposited on the cathode electrode 107 in the hole 112 perpendicularly to the cathode electrode surface by deposition, sputtering or the like. In that case, even if deposited perpendicularly, the cathode material is formed to have an inclined surface continuous to those of the metal layer 113 around the round holes 114. Thus, if the cathode material reaches a certain thickness, the holes 114 become closed. As a result, in the respective holes 112, conical, dot-like cathodes K each having a triangle cross section are formed on the cathode electrodes 107, respectively.
Thereafter, as shown in FIG. 19, the metal layer 113 and the cathode material formed on the layer 113 described with reference to FIG. 18 are removed. By doing so, dot-like cathodes K of conical shape, that is, each having a triangle cross section are formed in the holes 110 on the band-like, that is, stripe cathode electrodes 107, respectively.
The insulating film 108 exists around the cathodes K, whereby the cathodes K are electrically isolated from the cathode electrodes 107 and a cathode structure is constituted such that the gate electrodes 109 having electron beam transmitting holes formed out of the above-stated small holes 111h to face the respective cathodes K are arranged.
In this way, the field emission type cathodes K are formed on the cathode electrodes 107, respectively. Further, the cathode structure having the gate electrodes 109 crossing above the cathodes K is arranged to face the white fluorescent surface 101.
In the display apparatus main body 102 constituted as stated above, high plate voltage which is positive relative to the cathodes is applied to the fluorescent surface 101, that is, the metal back layer 106. Besides, voltage with which electrons can be sequentially emitted from the field emission type cathodes at, for example, the crossings of the cathode electrodes 107 and the gate electrodes 109, is applied between the cathode electrodes 107 and the gate electrodes 109, for example, voltage of 100V is applied to the gate electrodes 109 with respect to the cathode electrodes 107 sequentially and according to the display contents. Thus, electron beams are directed toward the white fluorescent surface 101 from the tip end portions of the cathodes K.
As a result, a white picture having light emission patterns corresponding to the respective colors in a time-division manner is obtained from the display apparatus main body 102. In addition, synchronously with the time-division display, the color shutter 103 is switched to thereby fetch lights corresponding to the respective colors.
Namely, red, green and blue optical images are sequentially fetched, thus displaying a color image as a whole.
As stated above, in the planar display apparatus 100 of the conventional structure shown in FIG. 15, the field emission type cathodes K facing to the fluorescent surface 101 are formed to be conical and have a triangle cross section by the manufacturing steps described with reference to FIGS. 16 to 19, and the electric field is concentrated on the tip end portions of the cones to thereby emit electrons.
Nevertheless, as the present development of technology progresses, it is desired that the electron emission parts of the field emission type cathodes K constituting this planar display apparatus 100 are formed to be more efficiently sharp.
Furthermore, as already described with reference to FIGS. 16 to 19, if cathodes K are formed, the radius of curvature of the tip end portion of each cathode K is relatively low or several tens of nanometers, e.g., about 60 nm. To satisfy today""s high resolution, it is necessary to form a finer tip end portion so as to efficiently concentrate an electric field and to efficiently emit electrons.
Under the circumstances, the inventors of the present invention continued dedicated efforts and studies and have eventually provided a field emission type cathode, an electron emission apparatus and an electron emission apparatus manufacturing method capable of making the electron emission part of a field emission type cathode K constituting a planar display apparatus finer and sharper to allow concentrating the field more efficiently.
A field emission type cathode according to the present invention is a field emission type cathode arranged to face an electron application surface, characterized in that at least an electron emission part of the field emission type cathode is formed by thin plate-like conductive fine grains; and a plate surface direction of the thin plate-like fine grains of the electron emission part is arranged to be a direction mainly crossing the electron application surface.
An electron emission apparatus according to the present invention is an electron emission apparatus having field emission type cathodes arranged to face an electron application surface, characterized in that at least electron emission parts of the field emission type cathodes are formed by thin plate-like conductive fine grains; and a plate surface direction of the thin plate-like fine grains of the electron emission part is arranged to be a direction mainly crossing the electron application surface; and if an electric field is applied, electrons are emitted from end faces of the thin plate-like fine grains of the electron emission parts of the field emission type cathodes.
An electron emission apparatus manufacturing method according to the present invention is characterized by comprising the steps of: forming a photoresist pattern having predetermined holes on formation surfaces of field emission type cathodes constituting an electron emission apparatus; dispersing thin plate-like conductive fine grains into a solvent and making an coating agent; coating and drying said coating agent on said photoresist pattern; and removing said photoresist pattern, and in that a plate surface direction of said thin plate-like fine grains in said holes and on wall portions of said holes is arranged to be a direction mainly crossing said electron application surface.
According to the field emission type cathode of the present invention and the electron emission apparatus having the field emission type cathodes of the present invention as constituent elements, the electron emission parts of the field emission type cathodes are formed by thin plate-like fine grains and also the plate surface direction of the thin plate-like fine grains are arranged to be a direction mainly crossing the electron application surface. Thus, by applying an electric field to the field emission type cathodes, the electron beam emission parts are sharpened and the electric field is efficiently concentrated.